Apparatus for rifling gun barrel tubes by extrusion



R. W. HILTON Nov. 10, 1970 APPARATUS FOR RIFLING GUN BARREL TUBES BY EXTRUSION 3 Sheets-Sheet 1 Filed April 25, 1968 HQ HW Ham .5

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R. W. HILTON Nov. 10, 1970 APPARATUS FOR RIFLING GUN BARREL TUBES BY EXTRUSION Filed April 25, 1968 5 Sheets-Sheet 2 INVENTOR R. W. HILTON Nov. 10, 1970 APPARATUS FOR RIFLING GUN BARREL TUBES BY EXTRUSION Filed April 25, 1968 s Sheets-Shet 5 INVENTOR liu'lphwfiflinn ATTOR N EY$ D United States Patent US. Cl. 29-1.1 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for rifling gun barrel tubes by extrusion includes a die for squeezing down the tube to reduce the inside diameter thereof during one stroke of a press ram and automatically orienting the die relative to the rifling mandrel for cooperation therewith in maintaining concentricity of the inside and outside diameters during the opposite rifling stroke. The mandrel is self-rotating in the tube and includes grooves in a plurality of ribs for forming the rifling lands while the tube is drawn over the mandrel, which grooves can be varied as to angular relationship by changing the space between the ribs to produce deep or shallow rifiings with sharp and distinct geometry.

One object of this invention is to provide apparatus for rifling gun barrel tubes by radial extrusion of the lands, which is especially well adapted for rifling those tubes formed according to the teachings of my co-pending application for Self-Centering Die System for Precision Extrusion of Gun Tubes Ser. No. 705,389, filed Feb. 14, 1968.

It is another object of this invention to provide apparatus for rifling gun tubes which reduces the outside diameter of the tubes to design diameter during pass of the tubes in one direction respective to the apparatus and rifles the inside of the tubes during pass of the tubes in the opposite direction.

It is a still further object of this invention to provide a rifling mandrel which is self-rotating to produce the prescribed twist to the rifling while the tube is drawn over the mandrel during the rifling stroke.

It is still another object of this invention to provide for the mandrel a plurality of grooved ribs which through their spacing control the depth of the rifling land and its geometry.

The specific nature of the invention as well as other objects and advantages thereof will appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

FIG. 1 is a longitudinal cross-section of the rifling apparatus of this invention mounted on an energizing press and shows the press ram at the end of its inward sizing stroke with the draw die in its advanced position;

FIG. 2 is a vie-w similar to FIG. 1 but shows the tube partially drawn over the rifling mandrel at the beginning of the outward rifling stroke of the ram;

FIG. 3 is a perspective view of the rifling mandrel;

FIG. 4 is an enlarged fragmentary cross-sectional view showing the rifling in the tube; and

FIG. 5 is a schematic view of the rifling mandrel showing one of the series of grooves formed in the ribs and cross-sections of the ribs as indicated.

Shown in the figures is a die assembly 12 and a rifling mandrel 14 which cooperate in completing rifling 16 in a smooth bore tube 18 and assuring concentricity of the inside and outside diameters of the rifled tubes. The inside diameter of tube 18 is slightly larger than the largest outside diameter of mandrel 14 so that the mandrel may be insertable within the tube. Energy for the operation which forms rifling 16 by radial extrusion is provided by a horizontal press 20 having a fixed block 22 and a ram 24 displaceable in inward and outward strokes. Die assembly 12 is mounted on block 22 coaxial to the extended axis of ram 24 and includes a casing 26 for receiving tube 18 after being pressed through a draw die 28 in the die assembly as hereinafter described. Mounted on the free end of casing 26 is a holder 30 for a bar 32 that extends therefrom into the casing so that the axis of the bar coincides with the extended axis of ram 24. Holder 30 includes thrust bearings 34 arranged so that bar 32 is held against axial displacement but is free to rotate about its axis. Mandrel 14 is mounted on the free end of bar 32 coaxial therewith and so as to be located within die assembly 12 as hereinafter described.

Die assembly 12 includes a plate 36 fixed to block 22, a mount 38 for draw die 28 and a collar 40 which secures the mount to the plate for relative movement respective thereto between an advanced position, as shown in FIG. 1 and a retracted position, as shown in FIG. 2. Mount 38 is biased to the retracted position by four springs 42, two of which are shown in the figures.

Draw die 28 includes a throat 44 which is coaxial to the extended axis of ram 24 and which includes a cylindrical sizing section 46 having a diameter essentially the same as the design diameter of the outside circumference of tube 18. A conical extrusion section 48 leads to sizing section 46 from the end of draw die 28 into which tube 18 is injected by ram 24 and acts to squeeze down the outside diameter of the tube to the design diameter when passed through the draw die. At the same time, the inside diameter of tube 18 is reduced to a diameter smaller than the large diameter of mandrel 14 so as to provide suflicient metal for extrusion by the mandrel to form rifling 16 as hereinafter described. Die assembly 12 and mandrel 14 are so arranged that when mount 38 is in the advanced position, as shown in FIG. 1, sizing section 46 is located forwardly respective to the mandrel so that the inside and outside diameters of tube 18 are reduced after passing over the mandrel. When mount 38 is in the retracted position, sizing section 46 is located directly over mandrel 14, as shown in FIG. 2, and positioned to maintain the outside diam eter of tube 18 by opposing the compressive force of the mandrel against the inside of tube 18 when forming rifling 16. Also, sizing section 46 serves to guide tube 18 in its displacement to maintain concentricity of the inside and outside diameters thereof during the rifling operation.

Tube 18 is held to ram 24 by means of a chuck 50 having jaws 52 which are receivable by a channel 54 formed around one end of the tube.

Mandrel 14 is provided with three equally spaced ribs 56, all of which have an equal number of grooves 58, and an uninterrupted sizing ring 60 which is disposed on the end of the mandrel that faces toward ram 24. The outside surfaces of ribs 56 and sizing ring 60 are all centered on the axis of the mandrel. The diameters of the uninterrupted portions of ribs 56 are approximately the same as the design diameter of the bases of grooves 61 in rifling 16 and the diameter of sizing ring 60 is approximately the same as design diameter of the top surfaces of lands 62 of the rifling. Ribs 56 are each provided with a leading conical section 63 and sizing ring 60 is similarly provided with a conical section 64. Grooves 58 are symmetrically formed in ribs 56 and are arranged so that each of the grooves in one of the ribs is helically aligned with corresponding grooves in the others to form a groove series 66, one of which is shown schematically in FIG. 5. The helical angle of each of the series 66, noted at H in FIG. 5, is essentially the same as that of the design helix for land 62 of rifling 16, which is formed thereby, with compensation made for the proportionate lengthening of tube 18 when the rifling is formed therein.

As shown in FIG. 5, bases 70 for all of the grooves 58 in each of the series 66 are formed on a common flat plane YY which is normal to a diametrical plane XX that symmetrically intersects the center one of the grooves in the respective series. The walls of each groove 58 are parallel to helical axis AA of. the respective series 66. This provides means for changing and controlling the formation of the resulting rifling 16, as will be explained hereinafter, and facilitates the cutting of grooves 58 in the fabrication of mandrel 14. It is seen in the cross sections shown in FIG. 5 that with bases 70 of grooves 58 in each of the series 66 being on the same plane, and because of the curvature of the outside surface of mandrel 14, the depth of the grooves in the outside ones of ribs 56 is shallower at the greatest distance from plane XX and this determines the maximum depth of lands 62. Where helical angle H is constant, axial distance D between the center one of the ribs 56 and the outer ones controls the angular relationship of grooves 58, and consequently their distance from plane XX, in each of the series 66 and therefore the depth of the grooves and the amount of metal extruded thereinto to form lands 62. Moreover, corners 59 of lands 62, which are critical areas in the geometry of rifiing 16, are precisely formed by the novel configuration of grooves 58 because with this design, and the radial extrusion of the metal thereinto, corners 71 of the grooves in the outside ones of ribs 56, which are closest to plane X-X, are disposed so as to be open to the direct flow of metal thereinto. Inner surfaces 74 of lands 62 are finished to the design diameter thereof and burnished by sizing ring 60 with corners 59 thereof distinctly formed thereby.

OPERATION Tube 18 is rifled and sized by the rifling apparatus of this invention by mounting the end of the tube with channel 54 therein to chuck 50 of ram 24 so that jaws 52 engage the channel. Press 20 is then energized to activate ram 24 until the opposite end of tube 18 incloses mandrel 14 and is received by draw die 28. Further energizing of press 20 will push tube 18 through draw die 28 with the pressure caused by the reduction of the diameters of the tube overcoming the pressure of springs 42 so that mount 38, with the draw die therein, is displaced to its advanced position. Thus, the reduction process is achieved without interference by mandrel 14 with the inside diameter being reduced smaller than the large diameter of the mandrel, after passing thereby, as shown in FIG. 1.

When ram 24 reaches the end of its inward sizing stroke, it is immediately energized for its outward rifling stroke. At the beginning of this rifling stroke, the bias of springs 42 forces mount 38 to its retracted position as shown in FIG. 2. Thus, sizing section 46 of draw die 28 is positioned over ribs 56 and sizing ring 60. As the reduced diameter portion of tube 18 is drawn over mandrel 14, the uninterrupted sections of ribs 56, aided by conical sections 63 thereof, compress the contracted portions of the inner wall of the tube to squeeze the displaced metal radially into grooves 58 and combine it with the metal aligned therewith to form lands 62 of rifiing 16. Diametrical expansion of tube 18 by mandrel 14 is prevented by the opposition of draw die 28 to maintain an even flow of metal between the mandrel and die and thereby assist in maintaining concentricity of the inside and outside diameters of tube 18. Draw die 28 also acts to guide tube 18 during the rifiing stroke and thereby maintain the tube concentric with the draw die and mandrel 14. Concentricity of the inside and outside diameters of tube 18 is further aided by the precise concentric relationship of the inside and outside diameters of the tube before rifting achieved by the teachings of my aforereferenced copending application for Self-Centering Die System for Precision Extrusion of Gun Tubes.

After lands in rifling 16 pass through grooves 58 in series 66, the top surfaces of the lands are sized and burnished by sizing ring which also acts to definitely form the corners of the lands. Passage of the metal through the series 66 with the displacement of tube 18 during during the Iifling stroke produces a torque in mandrel 14 which is rotated thereby according to helical angle H of the series. The center one of the grooves 58 in each of the series 66 acts to stabilize the rifling twist.

Upon completion of the outward rifling stroke of ram 24, tube 18 is removed from chunk 50 and the ends trimmed to where rifling 16 is formed.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

I claim:

1. Apparatus for forming rifling in a gun barrel tube by radial extrusion of the rifling lands comprising, a mandrel provided with a plurality of grooves for receiving metal from the tube when flowed thereinto during relative movement of said mandrel and tube to form the lands, said grooves being arranged in multiple series each including at least three of said grooves symmetrically aligned along a helical axis determined by the design axis of the rifling, each of said grooves comprising a pair of walls disposed parallel with the helical axis and the respective bases of said grooves in each series being disposed in a common flat plane.

2. The apparatus as defined in claim 1 wherein said grooves are so related to each other that the grooves of a series associated with the central one of said grooves are equally disposed on opposite sides thereof and with respect to a diametrical plane which symmetrically intersects said central groove.

3. The apparatus as defined in claim 2 wherein said common fiat plane is disposed normal to said diametrical plane.

References Cited UNITED STATES PATENTS H. A. KILBY, JR., Primary Examiner US. or. xm. -281; 72-283 

